What does 15 metres of prominence actually mean?

It's the vertical distance a summit must drop before the ground starts rising again towards a higher point. Fifteen metres is about the height of a four-storey building — noticeable when you're walking, but not so substantial that it always feels like a separate mountain.

What's the difference between Vandeleur-Lynam and Hewitts?

The Vandeleur-Lynam list requires only 15 metres of prominence, while Hewitts demand 30 metres, effectively doubling the requirement. This means Vandeleur-Lynam includes subsidiary tops that Hewitts would exclude, making it more comprehensive but less selective.

Do all Vandeleur-Lynam summits count as proper mountains?

No, not by traditional standards. While all must be at least 600 metres high, 14 of them fall just short of the 2,000-foot mark that typically defines Irish mountains, and 52 are subsidiary tops rather than independent peaks.

The Classification Index

Vandeleur-Lynams and the 15-metre line between an Irish summit and a subsidiary top

The Vandeleur-Lynam list uses a 15-metre prominence threshold, low enough that it includes subsidiary tops alongside independent mountains. As at 31 December 2023 it contained 275 locations above 600 metres: 209 mountain summits, 14 hill summits just short of 2,000 feet, and 52 subsidiary tops with less than 30 metres of prominence.

3 November 20267 min read